RFR: 8333893: Optimization for StringBuilder append boolean & null [v15]

[Shaojin Wen]

On Tue, 23 Jul 2024 13:48:57 GMT, Chen Liang <liach at openjdk.org> wrote:

>> explicit array stores  has the overhead of boundary checking. If putCharsAt of StringLatin1 is not implemented based on Unsafe, the performance will be worse than StringUTF16.
>> 
>> Of course, this is a common problem. StringUTF16.putChar is equivalent to Unsafe.putChar, without boundary checking. I found in many test scenarios that the UTF16 version performs better than the StringLatin1 version.
>> 
>> We may need to change some StringLatin1 related implementations to use Unsafe, otherwise users will turn off COMPACT_STRINGS to improve performance.
>
> Thank you for telling what the blocking issue is here. Does C2 not merge the bound checks when it does the merge stores? Interesting, and I think a fix from their side should be the way to go.

MergeStore does not work when using StringUTF16.putChar, waiting for improvements from @eme64

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PR Review Comment: https://git.openjdk.org/jdk/pull/19626#discussion_r1688786926